If that doesn't work, you can try to revoke access to WEBSTA, and log back in again - visit https://www.instagram.com/accounts/manage_access/ (make sure you're logged in) - look for WEBSTA and click REVOKE - visit WEBSTA and log in again - after verifying account, try liking posts

Liking errors are usually temporary bugs. Sometimes, it could also be from Instagram's system, which we won't have control over.

Make sure that you aren't using any Instagram auto bots, as this may cause them to ban your account.